Standoff high voltage insulators



June 10, 1969 5. E. LUSK 3,449,508

STANDOFF HIGH VOLTAGE INSULATORS Filed May 19, 1967 Sheet of 2 n L'" l ,1 1r Ill rr, I I 11 1 ll 1 I I I 1 I,

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Sheet 2 of 2 G. E. LUSK STANDOFF HIGH VOLTAGE INSULATQRS I I L r r I 1" I a 1 E 1 June Fil'ed May 19, 1967 for:

United States Patent 3,449,508 STANDOFF HIGH VOLTAGE INSULATORS George E:- Lusk, Downers Grove, Ill., assignor to G & W Electric Specialty Co., Blue Island, 11]., a corporation of Illinois Filed May 19, 1967, Ser. No. 639,848 Int. Cl. H01!) 1.7/00, 17/16 U.S. Cl. 174212 3 Claims ABSTRACT OF THE DISCLOSURE The invention relates to insulators for high voltage switches and the like, and has reference in particular to standoff insulators of improved design particularly adapted for high voltage electrical devices and which may be molded from compression moldable resin compounds.

The main objective of the invention is to provide a moldable standoff insulator which can be substituted for the standard porcelain insulator as heretofore used. The leaded-in insert type bus supports of the standard porcelain insulator have a relatively low cantilever strength. The designs employing cemented cap bus supports have a low insulator surface creepage per unit length ratio. Some attempts have been made to produce standard insulators from compression moldable plastics with the inserts integrally molded in. Some success has been obtained with low voltage insulators. However, the high voltage class insulators have presented serious problems due to the large mass of insulation residing between the inserts from end to end. Shrink cracks inevitably develop in the plastic between the inserts during the plastic curing cycle. These cracks give the insulators a low ionization inception level and poor dielectric strength.

The attempts made to alter the filler content of the plastic compound to eliminate the cracks have not met with any considerable success. Further attempts have been made by way of larger bus supports using an epoxy resin and a casting process. However, the casting process is inherently slow and the labor involved is large, so that the cast resin bus supports have not been economically feasible.

For comparable sizes of porcelain bus supports, the standoff insulators of the invention have the advantages of high production rates with a minimum of labor content, higher cantilever strengths than the leaded-in insert porcelain design, higher ionization inception levels and equivalent dielectric strength with lower costs, and a high surface creepage to height ratio.

Another object of the invention is to provide standoff insulators of improved design which can be produced in molded form from suitable plastics or resins, which will have the mechanical strength consistent with their expected service load and which will make efiicient electrical use of the surrounding medium which, in the case of high voltage apparatus, is insulating grade mineral' oils or other non-combustible liquids or gases.

With these and various other objects in view, the invention may consist of certain novel features of construction and operation, as will be more fully described and particularly pointed out in the specification, drawings and claims appended thereto.

In the drawings which illustrate an embodiment of the device and wherein like reference characters are used to designate like parts FIGURE 1 is a sectional view showing in elevation a high voltage switch employing the standoff insulators of the invention;

FIGURE 2 is an elevational view showing the standofi? insulator of the invention in bolted relation to a top bus bar and a bottom supporting stringer;

FIGURE 3 is a front elevational view of a standoif insulator, the same embodying the improved features of the invention;

FIGURE 4 is a side elevational view of the insulator as shown in FIGURE 3;

FIGURE 5 is a horizontal sectional view taken substantially along line 5-5 of FIGURE 3; and

FIGURE 6 is a horizontal sectional view taken substantially along line 66 of FIGURE 3.

The high voltage switch of FIGURE 1 is typical of the electrical apparatus such as may employ the moldable standoff insulators of the invention. The switch mechanism is immersed in oil or similar noncombusitble liquid contained within the tank 10 having the lid 11. The electrical supply power cables 12 and 13 extend through the entrance members 14 and .15, and thus through the bottom wall 16 of the tank for electrical connection with the rocker arms 17 and 18. The said rocker arms have pivotal movement on the respective axes 20 and 21 and the said arms carry the cont-acts 22 at their opposite free ends. Actuation of the rocker arms will electrically connect the supply power cables 12 and 13 with the terminals 23 and 25, which terminals are fixed so as to depend from the bus bar 26. Metal stringers 27 and 28 are employed for supporting the bus bar 26 from the side walls of the tank, and two or more standoff insulators 30 are interposed between the supporting stringers and the bus bar. The right angle member 31 conducts the electrical current from the bus bar 26 to the tap conductor 32. The said tap conductor extends through the insulating bushing 33 and thus through the end wall 35 of the tank 10*.

Grounding lugs 36 and 37 are located on respective walls 34 and 35 of the tank, and the rocker arms can be rotated so that the contacts 22 thereof will engage the terminals 38 and 39 of said lugs. Additional terminals 40 and 41 are located between the rocker arms, being supported by the metal supporting stringer 42. One or more standolf insulators such as 30* are interposed between the supporting stringer 42 and the bus bar 44. When it is desired to electrically connect the supply power cable 12 to the supply power cable 13 the rocker arms are rotated to cause the contacts 22 thereof to engage the terminals 40 and 41.

Details as regards the physical shape and construction of the standoff insulator of the invention are shown in FIGURES 3, 4 and 5. The insulator is substantially square in shape, or in other words, box-like in form with the area of the four exterior walls being approximately the same. The top wall 45, the intermediate baffle wall '46, and the bottom wall 47 are joined together by the side walls 48 and 50. The ends of the box-like unit are open so that oil may flow through the unit from end to end, both above and below the intermediate wall 46. All of the walls are so connected and joined to one another as to form a unitary structure and one which may be easily formed from suitable materials by a simple molding operation.

The moldable plastic or resin compounds which have been found suitable for the present standoff insulators include the glass reinforced epoxy resin compounds, the mineral filled and/or glass reinforced polyester molding compounds, the glass reinforced phenolic molding compounds and other suitable compression molding plastic materials. When the insulator is formed from these compounds it has the desired mechanical strength and also the necessary dielectric strength to support line voltages plus expected overvoltages due to surges. The molding compounds also meet an additional requirement, namely the insulator unit is inert, or in other words, free from reaction even after long immersion in the insulating mediums.

The inside surface of the top wall and the inside surface of the bottom wall are provided with projections so as to facilitate the bolting of the standoif insulators to the supporting stringers and to the bus bars. As best shown in FIGURE 5 the projections are generally U-shaped and the same are positioned in a particular relation with the bolt receiving openings in the walls. The projection 52 which depends from the top wall 45 is associated in the manner of FIGURE 5 with the openings 53 and 54, the said openings extending through the top wall. The projection 55 which extends upwardly from the bottom wall has the association as best shown in FIGURE 6 with the openings 56 and 57.

'In FIGURE 2 the bus bar '60 is shown as extending at right angles to the side walls 48 and 50 of the standoff insulator 30. In securing the bus bar to the top wall, a met-a1 strip 61 is employed having contact with the undersurface of the top wall. The securing bolts 62 pass through openings in the bus bar, then through the openings 53 in the top wall and the threaded depending end of the bolts are threaded in the metal strip 61. In this instance the strip 61 extends from side wall 48 to side wall 50' and is thus disposed in a direction parallel with the bus bar. Accordingly, the bolts 62 pass through openings 53- as indicated by FIGURE 5. Also it will be observed that the metal strip 61 is positioned and located by having contact with the ends of the U-shaped projection 52. When the bus bar 60 extends in a direction parallel to the side walls, the metal strip is disposed in the same direction and accordingly, the openings 54 in the top wall are used. In this latter case one end of the metal strip is positioned by being located within the arms of the U-shaped projection 52.

For securing the bottom wall 47 of the insulator unit to the metal strap or supporting stringer 63, a similai arrangement is employed with a metal strip such as 6 being used and wherein securing bolts 65 pass through openings in the bottom wall. The metal strip 64 extend: parallel to the walls 48 and 50, and thus the bolt opening: 57 are utilized as indicated by FIGURE 6. Here again should the strap 63 to which the bottom wall of the insulator unit is secured extend at right angles to the side walls, then the metal strip 64 would likewise extend parallel and the openings 56 in the bottom wall of the unit would be used for receiving the securing bolts 65.

The insulator unit of the invention can be produced by simple molding operations with a minimum of labor for the maximum output. Most of the weaknesses inherent in the use of porcelain are eliminated by the compression moldable plastics and resins selected for the present insulator. This advantage is obtained without sacrificing any of the physical or electrical characteristics. Also the cantilever strengths obtained for the insulator unit are considerably higher than those for the leaded-in inserted porcelain design. As evident from FIGURES 1 and 2, the met-a1 strips 61 and 64 and the ends of the bolts 62 and 65 will be surrounded by the dielectric medium which is void free and hence has good ionization inception levels. An additional constructional feature of the insulator resides in the intermediate wall 46 which functions as a barrier plate. This wall prevents or completely eliminates the migration of suspended conductive particles in the insulating liquid medium under the influence of an electric field which is generally referred to as cataphoresis. The intermediate wall also provides the necessany internal creepage distances.

The invention is not to be limited to or by details of construction of the particular embodiment thereof illustrated by the drawings, as various other forms of the device will, of course, be apparent to those skilled in the art without departing from the spirit of the invention or the scope of the claims.

What is claimed is:

1. A standoff insulator of the character described, said insulator comprising a molded unit formed of compression moldable plastic materials, said unit being substantially box-like in shape and form and including a top wall, a bottom wall and an intermediate wall, a side wall at each side of the unit joining the top, bottom and intermediate walls to form an integral, unitary structure, said top and bottom walls each having two pairs of openings therein, said intermediate wall being impervious, and said unit having open ends to permit the presence of a liquid within the unit both above and below the intermediate wall.

2. A standoff insulator of the character as defined by claim 1, wherein a first projection is located on the underside of the top wall and which extends inwardly towards the intermediate wall, and wherein a second projection is located on the top surface of the bottom wall and which also extends inwardly towards the intermediate Wall.

3. A standoff insulator of the character as defined by claim 1, wherein the molded insulator unit is formed of plastic materials selected from the group consisting of glass reinforced epoxy resin compounds, mineral filled polyester molding compounds, glass reinforced polyester molding compounds and glass reinforced phenolic molding compounds.

References Cited UNITED STATES PATENTS 1,793,430 2/1931 Mayer. 1,831,858 11/1931 Haggard 52606 2,892,014 6/1959 Eichelberger 174-212 3,225,133 12/1965 Knoy 174171 X FOREIGN PATENTS 161,016 4/1921 Great Britain.

LARAMIE E. ASKIN, Primary Examiner.

US. Cl. X.R. 

